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Opinion BMJ 2025; 391 doi: https://doi.org/10.1136/bmj.r2043 (Published 06 November 2025) Cite this as: BMJ 2025;391:r2043

1. Celia McMichael, professor1,

2. Jon Barnett, professor1

3. 1School of Geography, Earth and Atmospheric Sciences, The University of Melbourne, Melbourne, VIC, Australia

In July 2025, the International Court of Justice (ICJ) delivered a landmark advisory opinion on the obligations of states in respect of climate change, affirming that states have binding legal obligations to prevent climate harm and protect human rights. The advisory opinion acknowledged that risks to human health and population displacement are among the “severe and far reaching” consequences of climate change and pose an “urgent and existential threat” (para 73).1 Indeed, the increasingly urgent challenge of migration related to climate change poses multiple risks to human health.2 In this opinion piece we argue that these risks can be managed for better, or left unattended for worse, and to this end we identify a range of responses.

The threats of climate change to human health include: exposure to heatwaves and extreme weather events; changes in agricultural and fishery yields; disrupted freshwater availability and quality; and altered geographic distribution and incidence of infectious diseases (such as malaria, cholera, and diarrheal illnesses).3 Between 2030 and 2050, at above 2°C of warming, climate change is expected to cause 250 000 additional deaths per year including from undernutrition, malaria, diarrhoea, and heat stress. At 4°C of warming this would rise to four million excess deaths per year.4 Experiences of climate change impacts and information about future impacts are also causing clinically noticeable anxiety and distress.5

The impacts of climate change also affect migration pressures and constraints, although the fingerprint of climate change on migration and the magnitude of its effect are contested and difficult to measure.6 Population health research on climate migration has focused primarily on threats to health for climate migrants who are forcibly displaced by the sudden onset of climate hazards such as extreme storms, floods, and wildfires. Forced displacement typically leads to increased health risks such as acceleration of the transmission of infectious diseases in crowded settings that have disrupted health systems.78 Climate change adaptation and disaster preparedness can help avoid the worst of these impacts.9 Yet, disaster risk planning and management must also prepare for forced displacement and adverse health outcomes from extreme events related to climate change.

Alongside these emergency situations are slower migration and mobility pathways related to climate change, which bring different health challenges and opportunities. Rising sea levels and coastal erosion are leading to a loss of habitable land in parts of Alaska and Fiji, leading to relocation of households and communities who have not been able to adapt in place. Planned relocation has complex and diverse health outcomes. For example, Akiak, in Alaska, is home to 462 residents of the Akiak Native Community, where relocation is underway due to severe flooding and riverbank erosion. A lack of funding has resulted in relocated homes not being connected to piped water and sewage yet, which is a substantial threat to health.10 This example might be a harbinger of things to come. The prospect of increasingly frequent community relocations would further stretch the capacity of governments trying to meet the health needs of people under a changed climate.

Migration can also be an adaptive response to slow onset climate challenges such as erosion, food insecurity, and water scarcity. For example, one study found that heat stress and the associated decline in agricultural income have increased out migration from rural Pakistan.11 Though there are documented risks to health in these migration contexts, this is not inevitable, because there is evidence that well managed migration, with a high degree of agency and support for migrants, can enhance human security and health.12

Despite the recent ICJ ruling, and many international and national climate policy frameworks that call for strategies to avert, minimise, and address displacement (eg, the 2015 Paris Agreement), at least 25 countries now have national climate policies that refer to migration as an adaptation strategy to be supported so as to protect lives, livelihoods, and wellbeing.13 The efficacy of these policies is yet to be seriously tested, but they are evidence that foresight and planning to manage the health risks of migration is possible. However, as with migrants who move for socioeconomic and political reasons, migrants who move in response to climate risks might move into areas that are also exposed to climate change risks. For instance, people moving to urban poor areas tend to be at greater risk of flooding, water insecurity, and extreme heat related to climate change. Moreover, many migrants work in outdoor manual jobs where they are exposed to health risks from extreme heat.14

The Falepili Union*,* signed in November 2023 between Australia and Tuvalu (a low lying island nation in the Pacific Ocean facing higher mean and extreme sea levels, stronger storms, rainfall variation, ocean acidification, and threats to coral reefs) is the first treaty that includes a provision for international migration to support climate change adaptation, allowing for up to 280 Tuvaluans (2.5% of the population) per year to move to Australia.15 At face value, migrants who move from Tuvalu stand to benefit from reduced exposure to risks related to climate change in Tuvalu, and might benefit from improved access to health services. However, migration for the purposes of climate adaptation is not a panacea for health, and migrants might face different health and climate risks once in Australia. These risks include exposure to bushfire danger and estuarine and coastal flooding fuelled by climate change, heat stress from living in poorly designed houses, heat stress from jobs exposed to heat (such as outdoor labour in the agricultural sector), and poor access to health services. Tuvaluans who have relocated to Australia could experience a decline in their wellbeing owing to dislocation from the homes and communities that underpin their psychosocial needs.16 Tuvaluans will most likely move to areas where housing is relatively cheaper, which coincides with areas with lower access to medical professionals and services.

Key measures of the effectiveness of our responses to climate change are the degree of forced migration (which can be alleviated by large reductions in emissions and large increases in support for people to adapt in place) and the health of those who move (which can be protected by policies that are well funded, plan for migration, and plan for the health and other psychosocial needs of migrants). These otherwise seemingly diverse responses are all justified by an approach to migration that is based on human rights. The ICJ case is one of a series of legal decisions for an approach to support those most at risk from climate change, including migrants, that is based on rights.1718 All people have a right to health, regardless of their citizenship, including people who are trapped by, forced to move by, or move in anticipation of climate change impacts.19

An approach to the health of climate related migrants that is based on rights entails assisting people to adapt in place so that migration is not inevitable; mainstreaming climate change into health policies and plans; providing healthcare that is resilient to climate change and inclusive of migrants; and action on the social determinants of health for populations that are vulnerable to climate change, including those who move. Importantly, the principle of transboundary harm imposes an obligation on those states that are responsible for high greenhouse gas emissions to support all states to meet the health needs of migrants.20

Footnotes

Competing interests: None declared.

Provenance and peer review: Commissioned, not externally peer reviewed.

References

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Alaska Institute for Justice, Alaska Native Science Commission, Akiak Native Community, Chevak Native Village, Chinik Eskimo Community, Native Village of Kipnuk, Native Village of Kwigillingok, & Native Village of Kwinhagak. Rights, resilience, & community-led adaptation: lessons from ten Alaska Native communities. Alaska Institute for Justice. 2024.

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